Presently, research continues on developing a method and an apparatus for producing high resolution copies and in particular enlargements from a silver halide based instant image recording medium. In a silver halide instant image recording medium, such as a diffusion transfer integral film unit, copies of the original image are presently produced by sensing the light reflected from the positive. Typically, light within the visible spectrum which illuminates the positive is reflected therefrom to be sensed in three color separated spectral ranges, such as red, green, and blue to produce a recorded image. The recorded image may then be high pass filtered to increase its sharpness and tonescale mapped to improve its color correlation to the original image. Copies produced according to this method, however, may have no better resolution than the original positive.
The limit of the resolution of the positive in diffusion transfer integral film is primarily due to the lateral diffusion of dye which is inherent to the development of an image within a diffusion transfer integral film. In one type of integral film, a pod within the film unit is ruptured, after exposure, and reagent is forced between the surfaces of a negative and an image receiving layer, forming a new stratum comprising white pigment, opacifying dyes, alkali, water, and polymeric thickener. In exposed areas of the film unit, the silver halide functions so as to immobilize the associated image dye. In unexposed areas of the film unit, mobile image dye migrates through the overlying layers of the negative and through the pigmented reagent layer to reach the image receiving layer where it is mordanted and immobilized.
Some of the mobile image dye does not migrate from locations in the negative, directly onto corresponding locations in the image receiving layer, but instead laterally diffuses through the negative and the reagent layer onto locations in the image receiving layer that are not orthogonal with their initial locations in the negative. This results in the positive having a reduced resolution and one that is substantially lower than the resolution associated with the negative.
The positive is then viewed through a transparent polyester support by light reflected from the white pigment layer while the higher resolution negative remains obscured behind an opaque support layer. Accordingly, copies of the positive have a lower resolution when compared with the resolution of the negative.